1. Field of the Invention
The present invention relates generally to wireless communications devices. More specifically, the present invention relates to power control algorithms for use in mobile communications environments.
2. Related Art
Mobile communications devices, such as wireless phones, are often employed in vehicles or other mobile platforms that travel at relatively high velocities. For example, mobile communications devices are often used in automobiles, trains, and airplanes that travel at speeds as fast as several hundred kilometers per hour.
In wireless communications environments, signals are often transmitted between a transmitter and a receiver across a fading channel. When the transmitter and the receiver have a relative velocity with respect to each other, signals received from such fading channels exhibit fluctuations in amplitude and phase. These fluctuations have a peak rate that is proportional to this relative velocity.
Many wireless communications systems employ power control algorithms to promote the efficient use of radio frequency (RF) energy. In a mobile communications environment, power control algorithms involve the transmission of power control commands from communications devices to base stations. When a particular device sends a power control command, it directs the base station to adjust the power of it transmissions designated for that particular device. Thus, base stations typically receive commands directing a power increase or commands directing a power decrease.
Conventional wireless communications systems employ algorithms where power control commands are transmitted at a fixed-rate. Unfortunately, for these fixed command rate systems, as the rate of amplitude and phase fluctuations varies, the effectiveness of these commands also varies.
Therefore, conventional systems that employ the transmission of power control commands at a fixed rate are unable to optimally control power levels at all velocity ranges. Thus, for such fixed-rate systems, communications devices receive signals having higher power levels than are necessary to fulfill specified quality of service requirements. As a consequence, base stations receiving fixed-rate power control commands transmit signals having excessive power that could otherwise be used to support additional communications devices. Accordingly, system capacity becomes wasted.
Accordingly, what is needed is a method and system for dynamically adjusting power control operations in response to a device's velocity.